6 research outputs found
Can Hardware Distortion Correlation be Neglected When Analyzing Uplink SE in Massive MIMO?
This paper analyzes how the distortion created by hardware impairments in a
multiple-antenna base station affects the uplink spectral efficiency (SE), with
focus on Massive MIMO. The distortion is correlated across the antennas, but
has been often approximated as uncorrelated to facilitate (tractable) SE
analysis. To determine when this approximation is accurate, basic properties of
the distortion correlation are first uncovered. Then, we focus on third-order
non-linearities and prove analytically and numerically that the correlation can
be neglected in the SE analysis when there are many users. In i.i.d. Rayleigh
fading with equal signal-to-noise ratios, this occurs when having five users.Comment: 5 pages, 3 figures, IEEE International Workshop on Signal Processing
Advances in Wireless Communications (SPAWC), 201
Massive MU-MIMO-OFDM Uplink with Hardware Impairments: Modeling and Analysis
We study the impact of hardware impairments at the base station (BS) of an
orthogonal frequency-division multiplexing (OFDM)-based massive multiuser (MU)
multiple-input multiple-output (MIMO) uplink system. We leverage Bussgang's
theorem to develop accurate models for the distortions caused by nonlinear
low-noise amplifiers, local oscillators with phase noise, and oversampling
finite-resolution analog-to-digital converters. By combining the individual
effects of these hardware models, we obtain a composite model for the BS-side
distortion caused by nonideal hardware that takes into account its inherent
correlation in time, frequency, and across antennas. We use this composite
model to analyze the impact of BS-side hardware impairments on the performance
of realistic massive MU-MIMO-OFDM uplink systems
Can Hardware Distortion Correlation be Neglected when Analyzing Uplink SE in Massive MIMO
This paper analyzes how the distortion created by hardware impairments in a multiple-antenna base station affects the uplink spectral efficiency (SE), with focus on Massive MIMO. The distortion is correlated across the antennas, but has been often approximated as uncorrelated to facilitate (tractable) SE analysis. To determine when this approximation is accurate, basic properties of the distortion correlation are first uncovered. Then, we focus on third-order non-linearities and prove analytically and numerically that the correlation can be neglected in the SE analysis when there are many users. In i.i. d, Rayleigh fading with equal sianal-to-noise ratios, this occurs when having five users
Linear Precoding with Low-Resolution DACs for Massive MU-MIMO-OFDM Downlink
We consider the downlink of a massive multiuser (MU) multiple-input
multiple-output (MIMO) system in which the base station (BS) is equipped with
low-resolution digital-to-analog converters (DACs). In contrast to most
existing results, we assume that the system operates over a frequency-selective
wideband channel and uses orthogonal frequency division multiplexing (OFDM) to
simplify equalization at the user equipments (UEs). Furthermore, we consider
the practically relevant case of oversampling DACs. We theoretically analyze
the uncoded bit error rate (BER) performance with linear precoders (e.g., zero
forcing) and quadrature phase-shift keying using Bussgang's theorem. We also
develop a lower bound on the information-theoretic sum-rate throughput
achievable with Gaussian inputs, which can be evaluated in closed form for the
case of 1-bit DACs. For the case of multi-bit DACs, we derive approximate, yet
accurate, expressions for the distortion caused by low-precision DACs, which
can be used to establish lower bounds on the corresponding sum-rate throughput.
Our results demonstrate that, for a massive MU-MIMO-OFDM system with a
128-antenna BS serving 16 UEs, only 3--4 DAC bits are required to achieve an
uncoded BER of 10^-4 with a negligible performance loss compared to the
infinite-resolution case at the cost of additional out-of-band emissions.
Furthermore, our results highlight the importance of taking into account the
inherent spatial and temporal correlations caused by low-precision DACs
Distortion-Aware Linear Precoding for Massive MIMO Downlink Systems with Nonlinear Power Amplifiers
We introduce a framework for linear precoder design over a massive
multiple-input multiple-output downlink system in the presence of nonlinear
power amplifiers (PAs). By studying the spatial characteristics of the
distortion, we demonstrate that conventional linear precoding techniques steer
nonlinear distortions towards the users. We show that, by taking into account
PA nonlinearity, one can design linear precoders that reduce, and in
single-user scenarios, even completely remove the distortion transmitted in the
direction of the users. This, however, is achieved at the price of a reduced
array gain. To address this issue, we present precoder optimization algorithms
that simultaneously take into account the effects of array gain, distortion,
multiuser interference, and receiver noise. Specifically, we derive an
expression for the achievable sum rate and propose an iterative algorithm that
attempts to find the precoding matrix which maximizes this expression.
Moreover, using a model for PA power consumption, we propose an algorithm that
attempts to find the precoding matrix that minimizes the consumed power for a
given minimum achievable sum rate. Our numerical results demonstrate that the
proposed distortion-aware precoding techniques provide significant improvements
in spectral and energy efficiency compared to conventional linear precoders.Comment: 30 pages, 10 figure